Laterals are kicked off in an open hole well with a whipstock/billet/billet supported on an anchor. The whipstock/billet slide has an inclined face that can direct the gauged hole bit to start a lateral in the proper orientation, the aluminum billet is round with a pocket notched at the top to help start bi-center bits. Known orientation tools are used to insure the proper positioning of the whipstock/billet/billet face. The whipstock/billet, after being properly oriented is normally secured by an anchor assembly, open hole anchors in the past did not have a adjustable fulcrum point, this tool not only anchors the whipstock/billet/billet but also forces the top of the whipstock/billet/billet to the formation wall holding the whipstock/billet/billet secure in the desired direction. Typically the slips that are part of the anchor assembly are actuated to move radially outward. The slips are normally around the periphery of the anchor body and when actuated secure putting the anchor and attached whipstock/billet/billet in the center of a cylindrical wellbore.
In open hole applications the slips of the anchor bite into the formation. When anchors in the past were actuated, for example in open hole, the upper end of the whipstock/billet/billet was centered in the surrounding wellbore. When the drill bit was advanced to drill the lateral its interaction with the top of the whipstock/billet/billet that was unsupported by the surrounding well bore can cause vibration on the anchor slips causing them lose the grip on formation. As a result the whipstock/billet/billet was without support and could slip down the well bore. At that point drilling had to stop a sidetrack has to be done above the whipstock/billet/billet process repeated, or the well was plugged back to a kickoff point with cement this adds additional time and incremental increase to the drilling cost. This proved to be troublesome in the past particularly in open hole applications.
FIGS. 1 and 2 illustrate the problem with the prior designs. FIG. 1 shows a whipstock/billet 10 without the running string that would normally deliver it and help set the anchor 12 that is below it. FIG. 1 illustrates a vertical bore 14 but the same result will occur in a deviated bore. An open hole 14 is illustrated as opposed to a cased hole. The anchor 12 has upper slips 16 and lower slips 18 that are disposed around the outer periphery and generally in a symmetrical manner. The gripper teeth 20 and 24 have opposed orientations to hold the whipstock/billet 10 in wellbore 14 against applied forces that may come in opposed directions. When the setting tool (not shown) is actuated to set the anchor 12 the slips 16 and 18 tend to center the whipstock/billet 10 in the wellbore 14 as indicated by the annular gap 26 shown in FIG. 2 representing the set position. One reason this occurs is that the slips 16 and 18 are close to each other and move out at the same rates. Those skilled in the art will appreciate that a passage 28 is used for actuation of anchor 12 and after actuation leaves a passage that can provide access to the wellbore below the whipstock/billet 10.
The problem with this design is that the whipstock/billet is a very long and slender structure that is subjected to complex loading when engaged by a rotating bit. When centered in a wellbore it has no lateral support and acts akin to a cantilevered beam subjected to torsion and lateral loads. As a result, grip failures have occurred in the past.
The present invention addresses the issue with a grip system with offset grippers that initially push in a given direction laterally below a whipstock/billet so as to cant or cock the opposite end of the whipstock/billet against the wellbore whereupon that position is then locked in by another set of slips spaced from the initial slip or slips vertically as well as circumferentially, in the preferred embodiment. Additionally, the anchor of the present invention can support a downhole tool above and a tubular string below and be actuated to support both while also allowing fluid communication through the tool, such as a whipstock/billet or a billet, to the tubular string below. These and other aspects of the invention will be readily appreciated by those skilled in the art from a review of the description of the preferred embodiment, the drawings and the claims which appear below.